How do you add multiple colors to one object
Oh! Good question! This is so easy, that it should probably be used a lot more than it is on objects.

I assume you know how to create the color materials for objects, so I won't address that. Every time you go to the materials tab to make a new material, you click the "+" or "Add" button. You can do that many times. So, go ahead and create the materials you need.

BTW, the method I describe here is SO simple, but, the best way is to absolutely UV edit. Whew! What a chore. I prefer this stupid simple method.

What you do next is simply go into "Edit Object" mode, and use the "face" selection. Select the faces you want of the particular material. Select the proper material from the list of materials I advised you to create above, and click that "Assign" button. Select the faces you want of a different material, and, from that same list of materials, "Assign" the appropriate material to those faces. Stupid simple, no?